How do I curve a section of a model?
This can be done by selecting the bottom two vertices, pressing O, and moving them in the desired direction (be sure to put it on the Sharp falloff type and make the radius large enough using Scroll):





Although you can do this, I would recommend making the switch as if it was in between the two states, so it is symmetrical. You can then easily rotate it.



Start by forming the switch profile. Add a circle with 12 vertices, and in edit mode select all and press S-Y-2, then press Enter to finish. Now select all except the bottom vertices and delete them. 



Now you can extrude downwards using E, Z. When scale the new vertices to zero along the zed axis by pressing S-Z-0. Now scale along the Y axis as desired (S-Y).



Now extrude the outline to the desired width using E.



Now you can delete half of the vertices.



And add a Mirror Modifier:



Make sure you select the right Axis, either X, Y or Z. In this case it is Y.

Now any changes you make to the one half are exactly mirrored to the other half. Also, this piece can be rotated easily to animate the switch if ever necessary. 

Things you might want to consider:


Bevel modifier/Sub-Division modifier
Re-calculate Normals (Edit mode Ctrl+N)


This should get you a good base mesh to work with, from which you can add specific details.